This invention relates to head positioning mechanisms for rotating memories and, more particularly, to band drive actuators for rotating magnetic memories and the like.
Rotating memories, such as rigid and floppy disk drives, usually have a head positioning mechanism (commonly referred to as an "actuator") for selectively repositioning one or more read/write heads radially relative to a rotating recording medium so that data may be transferred to or from any selected one of a plurality of concentric data tracks on the recording medium. Band drive actuators have been successfully employed, especially in floppy disk drives which have traditionally been able to accommodate relatively large head positioning errors. Now, however, floppy disk drives and other lower cost rotating memories are being designed to obtain increased track densities. Consequently, increased head positioning accuracies are being required.
Prior band drive actuators have typically included a head/carriage assembly which is mounted for sliding movement on a guide rail. In such an actuator, a nonextensible tensioned band is wrapped around and secured to a capstan which, in turn, is pinned to the output shaft of, say, a drive motor. Moreover, the opposite ends of the band extend in opposite directions from the capstan and are fastened to spaced apart points on the head/carriage assembly so that the head/carriage assembly moves back and forth on the guide rail depending on the direction of rotation of the capstan. See, for example, U.S. Pat. No. 4,161,004, which issued July 10, 1979 for a "Head Positioning Mechanism for Recording/Playback Machine".
Unfortunately, the sliding friction between the head/carriage assembly and the guide rail creates a mechanical hysteresis which limits the head positioning accuracy that can be achieved with a conventional band drive actuator. Accordingly, relatively complex and expensive actuators having precision ball bearing supported head/carriage assemblies are still widely utilized, even though they classically require six or so precision ball bearings and several fixed precision rail surfaces.